New, more readily visualized metal cluster complex immunoprobes will be developed, labeled with platinum or palladium complexes 1.8 nm to 3.6 nm in diameter or with multiple gold cluster complexes. These probes will combine the easy visualization of 3 nm colloidal gold with the advantages of molecular coordination complexes: high penetration, no non-specific protein binding, and site-specific covalent label conjugation. Novel modified ligands will be used to impart high watersolubility and biological compatibility to both the platinum and palladium compounds and the gold clusters. Multiple undecagold and 1.4 nm Nanogold cluster complexes will be combined in a single larger label, up to 8 nm in diameter, using starburst dendrimer molecules as carriers; these will be coupled to antibodies to give unprecedented sensitivities with silver enhancement, possibly an order of magnitude or more higher than with current methods: these will be tested as components of highly sensitive automated diagnostic immunoassay systems. Novel dendrimers comprising adamantylic initiator cores and chain branching monomers, and rigid rod spacers will be synthesized and investigated as carriers for multiple gold clusters, and will also be studied as precursors to new "designer" host materials for guest incorporation. PROPOSED COMMERCIAL APPLICATION: New classes of 2-8 nm metal cluster immunoprobes will be developed which combine the easy visualization of the smaller (1-5 nm) colloidal gold probes with the low non- specific binding and superior tissue penetration of the smaller gold cluster probes. They are expected to be widely used in electron microscopy and may show unprecedented sensitivity in diagnostic immunoassays The new labels will be developed as site- specific labeling reagents, and may be precursors to novel catalysts and materials.